1. Field of the Invention
The present invention relates to a micro-strip antenna which can be used to receive satellite broadcasts, etc.
2. Prior Art
The conventional antenna shown in FIG. 5 is known as a micro-strip antenna. In this antenna, a dielectric 20 is installed on a grounding conductor 10, and a radiating conductor 30 such as copper foil, etc. is installed on the dielectric 20. Ordinarily, a substrate having copper foils on both sides of a dielectric is used as a micro-strip antenna. More specifically, a dielectric is sandwiched between two pieces of copper foils, and a copper foil on one side of the dielectric is used as the grounding conductor 10, and a copper foil on the other side is used as the radiating conductor 30 after being etched into a prescribed shape.
The center frequency of the micro-strip antenna varies depending upon the length of one side of the radiation conductor 30, the thickness of the dielectric 20, the dielectric constant of the dielectric 20, and other factors.
Normally, the reception frequency band width of a micro-strip antenna is 1 to 2% of the center frequency of the band to be received, and if errors occur somewhere in the material management and during the manufacturing process, etc. of the antenna, the center frequency may shift, causing the transmission frequency of satellite broadcasts not to fall within the reception band of the micro-strip antenna. For example, if a substrate having a dielectric constant of 2.6 is used as the dielectric so that the antenna's center frequency is 575 GHz and the dimensional precision is set at 200 microns, then the center frequency can shift as much as 10 MHz. If the center frequency of the reception frequency band is 1,575 MHz, the band width of such a frequency is in the range of 15.75 to 31.5 MHz, and if the dimensional precision of the antenna drops and other conditions affect the antenna, the center frequency of the micro-strip antenna would further shift so that the transmission frequency of satellite broadcasts never fall within the reception frequency band of the antenna.
Thus, conventionally, it is difficult to manufacture micro-strip antennas with a uniform center frequency.